1. Field of the Invention
The invention relates to a device for moving a first object relative to a second object, which device comprises a first part, which can be fixed to said first object, and a second part, which can be fixed to said second object. Such a device may be used for moving bone portions relative to each other inside a human or animal body, whereby said first object is a first bone portion and said second object is a second bone portion.
Although the invention is not limited to medical applications, the present specification will describe the implementation of the invention for the movement of bone portions relative to each other inside a human body.
2. Description of Related Art
Devices are known wherein two bone portions are connected by means of pins to an elongation apparatus present outside the body, which moves the pins in such a manner that the desired movement is effected at the desired speed of the bone portions. One drawback of such external fixation devices is that they constitute a considerable physical and psychological burden for the patient, and that there is moreover a constant risk of infection in several places where the skin is pierced by pins.
Furthermore devices are known which can be implanted into the human body and which comprise a drive motor which moves the two bone portions to the desired extent relative to each other. Such a device is known from U.S. Pat. No. 5,415,660, which publication describes an elongation pin comprising two ends, which are each fixed to a bone portion, whilst the elongation pin is capable of telescoping out, thus elongating the pin. The drive motor used for said elongation thereby consists of a shape memory metal, whose shape is dependent on the temperature, as will be explained in more detail as yet.
A device for moving bone portions relative to each other, which is to be implanted into the body, must exhibit a high degree of reliability, which can be achieved by reducing the number of parts to a minimum. In addition to that the device must have small dimensions. Furthermore it may be necessary that the device is capable not only of moving the two bone portions in a direction away from each other, but also towards each other to a desired extent. The latter may for example be important if, for whatever reason, the bone portions have been moved too much or when it becomes necessary at a certain point in time to release or reverse the load being exerted on the tissue of the human body.